The present invention relates generally to roof ventilating systems, and particularly to roof ventilating systems for commercial and industrial buildings, that typically have substantially flat roofs.
A typical commercial roof includes a structural roof deck, covered by a vapor barrier. A layer of insulation is placed over the vapor barrier. An impermeable synthetic plastic roofing membrane is placed over the insulation. Water leaks from above the membrane may wet the insulation or water from inside the building may condense between the vapor barrier and the plastic roofing membrane and wet the insulation. Wet insulation has a reduced heat transfer resistance and can degrade.
Vents are used above the building roof membrane to vent the space between the membrane and the vapor barrier. With effective roof venting, wet roofs can be dried over a period of time.
Another problem with membrane covered flat roofs is that a strong wind flowing across the membrane creates a suction that tends to lift the membrane up off of the roof structure. The present inventor has recognized that roof vents, if in air flow communication with the space beneath the membrane, transfer the suction force caused by the wind to an underside of the membrane and tends to pull the membrane down onto the roof structure in the vicinity of the vent.